1. Field of the Invention
The present invention relates to imaging devices equipped with an imaging function, such as electronic cameras e.g. digital cameras, and particularly to imaging devices which control data communication with external recording devices connected thereto.
2. Description of Related Art
When connecting a typical electronic camera and the like to other devices, it is usually connected through a USB (Universal Serial Bus) interface. According to the USB standard, a host which has a host controller polls (queries) a device connected to the host, thereby performing the communication between the host and the device. All the communications are controlled by the host and thus the devices cannot poll the host.
Generally, when transferring imaging data obtained by an imaging operation of an electronic camera to an external recording device through a USB cable, the electronic camera is connected to a personal computer (PC) which is connected to the external recording device and then the imaging data is transferred to the external device via the PC. Therefore, the PC is the host and the electronic camera and the external recording device are the devices. The PC controls all the communications and transfers the imaging data from the electronic camera to the external recording device. Thus, transferring imaging data taken with an electronic camera to an external recording device always needs the intermediary of PC, which requires vexatiousness of starting PC and the like.
There has been proposed an imaging device capable of performing data communication with an external device without the intermediary of PC.
Generally, when a host equipment and a device equipment are connected to each other through a USB interface, the host equipment and the device equipment send a query command and a reply command to each other in conformity with the USB standard to thereby establish the connection therebetween. Also, when the connection between the host equipment and the device equipment is canceled, the host equipment and the device equipment send a query command and a reply command to each other in conformity with the USB standard to thereby cancel the connection therebetween. Thus, in the case where an external recording device as the device equipment is connected to the host equipment, and the connection is established between the both equipments, if the user unplugs a USB connector from one of the equipments in error and thereby physically disconnects the equipments, then the stored data recorded in the external recording device can be destroyed.
However, in the conventional imaging device capable of performing data communication with an external device without the intermediary of PC, no countermeasures are taken to prevent stored data recorded in the device equipment from being destroyed by physical disconnection in the connection established status as described above.